1. Field of the Invention
The present invention relates to a multimedia conference system and method utilizing Internet to establish a communication between a originating unit and a receiving unit, and more specifically, a multimedia conference system and method that enables direct communication between user agents in the private network and users from the Internet by connecting public network (Internet) and local area network (private network).
2. The Background of the Invention
Up to now, the Internet has been developing mainly in the field of data traffic such as an e-mail (electronic mail) or web, and with the advent of applications requiring transfer of real-time traffic, such as distant learning and teleconference, the Internet is now progressing on the trend to support real time traffic such as voice and image.
The SIP (Session Initiation Protocol) system operating on the basis of the IP (Internet Protocol) consists of a user agent and a network server. The user agent is a terminal, generally functioning as a UAC (User Agent Client) for requesting a call and a UAS (User Agent Server) for responding to a requested call.
The SIP makes use of the existing Internet servers such as the existing Name Server, Authentication server as they are, referring to overall procedures regarding a call session establishment, maintenance, release, and management for the Internet phone. The SIP is a protocol based on a client-server, and develops in such form that a call trying part calls a counterpart in order to get the counterpart to attend a call session. Therefore, the SIP provides functions such as a user position locating, session establishing, session negotiating, session participant managing, and a Call Feature Invocation, including Hold, Transfer, and Mute. Also, for processing a call, the SIP uses a protocol based on a text having syntax and semantics similar to HTTP (Hyper Text Transfer Protocol).
However, the SIP and the associated media protocol (e.g. RTP), which are the key enabler of new multimedia over IP services, are blocked by Firewalls and network address translation (NAT) devices, which are typically deployed on IP network boundaries to perform security service.
Firewalls deployed on the boundary of the local area networks are generally configured to block all unsolicited inbound traffic, thus preventing the entry of SIP-controlled media traffic.
NATs translate IP address and port numbers in private address ranges into public address when traffic flows from a private network to public network. This allows a limited number of public IP addresses to serve for the needs of even the largest corporation. Each device in the private network has its own private IP address. Traffic sent to a device on the public network will be dynamically assigned a specific port number at the public address by the NAT. The NAT maintains a “table” that links private address and port numbers to public port numbers and IP addresses.
With NAT on the boundary of the local area network, initiating an outbound connection is easy; on the other hand, receiving an incoming call is more difficult. The reason is that the internal extension numbers are non-routable from the public network. Users dialing in must be routed to an attendant to be connected to the correct extension. Clearly in the case of a NAT, there is no equivalent for an attendant, so unsolicited incoming calls cannot be supported.
The methods to solve the problems related to NAT are described in Newport network, “Solving the Firewall and NAT Traversal Issues for Multimedia Services over IP” and “Enabling Customers to Connect”, incorporated herein for reference.